Honestly, I upvote pretty much anything that meets the bar of "this looks vaguely interesting and might be something I'll want to read one day." That is, I use upvote more as a way of bookmarking things, than as any kind of endorsement or sign that I think anybody else should be interested in the content.

Yes, I know there is a "favorite" feature, but using that requires one extra click, so...

I use "favorite" as a bookmark. Just recently I discovered how to do so.

Anything interesting that I do not come across in the mainstream media

Anything Computer Graphics and tools and websites that i personally have used. I upvote roughly 3 times a week and flag 1 post a month. I visit the homepage multiple times on a day.

edit) I also block a lot of links that are on hackernews. My blocking script removes about 1 to 5 links from the homepage. I use ublock origin with the following trick

news.ycombinator.com##table.itemlist > tbody > tr.athing:has-text(/ PaaS /)

news.ycombinator.com##table.itemlist > tbody > tr.athing:has-text(/ PaaS /)+tr

The words That I block are the following:

PaaS, ISP, ISPs, sell, city, F#, Delphi, Covid-19, PEP, Perl, Amazon, Apple, Microsoft, DNS, Face ID, Touch ID, iOS, SaaS, ECommerce, DRM, firmware, Zoom, LinkedIn, WhatsApp, Twitter, Quora, Instagram, Facebook, Uber, TikTok, AWS, GraphQL, Business Model, drugmakers, police, Cloud, Heroku, FreeBSD, Java, Swift, startup, java, React, Angular, Show HN:, Launch HN:, hiring, GPS, Hiring, techcrunch.com, .js, advertising, Caddy, cybernetics, Clojure, leaders, CS50, vice.com, ycombinator.com,